Phosphorous doping in vertically aligned ZnO nanorods grown by wet-chemical method
TL;DR: In this paper, the synthesis of well-aligned highly crystalline phosphorous (P) doped ZnO nanorods (ZnO:P) on glass substrates is demonstrated.
Abstract: The synthesis of well-aligned highly crystalline phosphorous (P) doped ZnO nanorods (ZnO:P) on glass substrates is demonstrated here. Vertically aligned ZnO nanorods are fabricated by a two-step method comprises of nanocrystalline ZnO seed layer formation by dc sputtering technique followed by solution growth of ZnO nanorods. To incorporate P, aligned ZnO nanorod films are exposed to P vapor in a vacuum chamber and then subjected to rapid thermal annealing in vacuum at an elevated temperature of 450 °C. Scanning electron microscopy and X-ray diffraction measurement confirm the growth of highly crystalline well aligned hexagonal ZnO nanorods that are perpendicular to the substrate surface. The optical band gap estimated from the transmittance spectra recorded by a UV–VIS–NIR spectrophotometer is 0.24 eV lower for ZnO:P compared to ZnO nanorods. Vibrational properties of ZnO:P nanorods are studied by FTIR and Raman spectra. Raman peak appeared at 355 cm −1 for ZnO:P is due to the Zn-site substituted by phosphorous. For ZnO nanorods, the room temperature photoluminescence (PL) spectra shows a sharp UV emission peak due to near band edge transition and a broad blue–green emission peak due to defect related transition. The observed red shift for the UV emission peak in the ZnO:P nanorods is associated with the shrinking band gap whereas the intense and broad blue–green emission peak is due to defects introduced with P doping.
Citations
More filters
TL;DR: In this article, a solution processed transparent thin films of graphene oxide (GO) and zinc oxide (ZnO) in different compositions prepared by a simple two-step chemical synthesis method have been studied for their UV detection properties.
Abstract: All solution processed transparent thin films of graphene oxide (GO) and zinc oxide (ZnO) in different compositions prepared by a simple two-step chemical synthesis method have been studied for their UV detection properties. The preparation of GO through oxidation of graphite flakes is followed by sol–gel spin coating deposition of the GO–ZnO composite films on glass substrates. The surface morphology, microstructure and composition of the samples have been studied to confirm the formation of composite thin films comprising wurtzite-ZnO nanocrystallites and GO flakes. Optical studies demonstrate that both the transparency and optical band gap of the samples as estimated from wavelength dependent transmittance curves decrease with the increase of GO content in the films, while the charge carrier concentration increases by 5 fold. The in-plane current–voltage (I–V) measurements with two silver electrodes on the GO–ZnO film show a significant enhancement of the photosensitivity in comparison to ZnO films when they are exposed to UV light of different intensities. The response time (t90-response) is nearly three times smaller for GO–ZnO composite films as compared to that of pure ZnO. This improvement is attributed to the defect state modulation and carrier density improvement of the thin films with incorporation of GO, which is encouraging to propel optical, electrical and hence optoelectronics applicability of ZnO composite based transparent devices.
79 citations
TL;DR: In this article, the photocatalytic properties of doped semiconductors were investigated using microwave assisted hydrothermal and modified polymeric precursor methods of synthesis, and density functional theory calculations were employed to determine specific features related to electronic structure, morphology, and photocatalysis.
64 citations
TL;DR: In this article, the effect of pH and nitrate concentration on the size and morphology of prepared ZnO nano-rods have been investigated by particle size distribution analysis and field emission scanning electron microscopy respectively.
Abstract: ZnO nano-rods were synthesised via wet chemical method at different nitrate concentration and pH value. The effect of pH and nitrate concentration on the size and morphology of the prepared ZnO photocatalysts have been investigated by particle size distribution analysis and Field emission scanning electron microscopy respectively. Additionally, UV-Visible spectroscopy and energy dispersive studies and were carried out to confirm the optical and compositional properties of the prepared ZnO powder. The estimated band gap of the as prepared ZnO photocatalysts at different pH and nitrate concentration calculated on the basis of Kubelka–Munk function was found to be in the range of ∼ 2.7–3.6 eV. Field emission scanning (FE-SEM) and transmission electron microscopic (TEM) observations reveal rod-like morphology. The photocatalytic activity of prepared ZnO photocatalysts was evaluated by photo degradation of the mixture of Methylene Blue (MB) and Rhodamine 6G (Rh 6G) solution under simulated solar radiation. Volume of hydrogen evolution was recorded in the presence of prepared ZnO photocatalysts in 2 h. Nitrate concentration, and pH value showed a significant effect on the optical and morphological behaviour of the prepared ZnO powdered photocatalysts.
47 citations
TL;DR: In this article, the chemical synthesis of a hetero-junction solar cell in superstrate configuration using nanocrystalline p-type Cu2ZnSnS4 (CZTS) as absorber layer, vertically aligned n-type ZnO nanowire array as window layer and very thin ZnS as buffer layer was reported.
32 citations
TL;DR: A detailed review on various nanostructures of ZnO as photocatalyst has been carried out to explore the role of structural engineering in improving the photocatalytic performance under various irradiation conditions as mentioned in this paper.
Abstract: Effective solar energy harvested through material engineering is a promising technique for both environment and energy applications. Current researches show the role of metal oxide photocatalyst for efficient solar energy harvesting. Among various techniques for improving the photocatalytic performance, structural engineering is one of the effective methods to enhance the surface area and photon absorption of the metal oxide along with effective charge carrier separation. Keeping this in mind, a detailed review on various nanostructures of ZnO as photocatalyst has been carried out to explore the role of nanostructures in improving the photocatalytic performance under various irradiation conditions. The review reveals that structural engineering can enhance the photocatalytic performance of ZnO drastically compared to the conventional one. This perceptive article helps to understand the role of structural engineering in enhancing the photocatalytic performance of ZnO.
32 citations
References
More filters
TL;DR: In this paper, the authors used a Geiger counter spectrometer to measure the changes in intensity distribution in the spectra of cold worked aluminium and wolfram and found that the line breadths may be attributed to simultaneous small particle size and strain broadening, the latter predominating at the higher Bragg angles.
7,802 citations
TL;DR: In this article, the status of zinc oxide as a semiconductor is discussed and the role of impurities and defects in the electrical conductivity of ZnO is discussed, as well as the possible causes of unintentional n-type conductivity.
Abstract: In the past ten years we have witnessed a revival of, and subsequent rapid expansion in, the research on zinc oxide (ZnO) as a semiconductor. Being initially considered as a substrate for GaN and related alloys, the availability of high-quality large bulk single crystals, the strong luminescence demonstrated in optically pumped lasers and the prospects of gaining control over its electrical conductivity have led a large number of groups to turn their research for electronic and photonic devices to ZnO in its own right. The high electron mobility, high thermal conductivity, wide and direct band gap and large exciton binding energy make ZnO suitable for a wide range of devices, including transparent thin-film transistors, photodetectors, light-emitting diodes and laser diodes that operate in the blue and ultraviolet region of the spectrum. In spite of the recent rapid developments, controlling the electrical conductivity of ZnO has remained a major challenge. While a number of research groups have reported achieving p-type ZnO, there are still problems concerning the reproducibility of the results and the stability of the p-type conductivity. Even the cause of the commonly observed unintentional n-type conductivity in as-grown ZnO is still under debate. One approach to address these issues consists of growing high-quality single crystalline bulk and thin films in which the concentrations of impurities and intrinsic defects are controlled. In this review we discuss the status of ZnO as a semiconductor. We first discuss the growth of bulk and epitaxial films, growth conditions and their influence on the incorporation of native defects and impurities. We then present the theory of doping and native defects in ZnO based on density-functional calculations, discussing the stability and electronic structure of native point defects and impurities and their influence on the electrical conductivity and optical properties of ZnO. We pay special attention to the possible causes of the unintentional n-type conductivity, emphasize the role of impurities, critically review the current status of p-type doping and address possible routes to controlling the electrical conductivity in ZnO. Finally, we discuss band-gap engineering using MgZnO and CdZnO alloys.
3,291 citations
TL;DR: In this paper, the authors used a new technique to fabricate p-type ZnO reproducibly, and showed high-quality undoped films with electron mobility exceeding that in the bulk.
Abstract: Since the successful demonstration of a blue light-emitting diode (LED)1, potential materials for making short-wavelength LEDs and diode lasers have been attracting increasing interest as the demands for display, illumination and information storage grow2,3,4. Zinc oxide has substantial advantages including large exciton binding energy, as demonstrated by efficient excitonic lasing on optical excitation5,6. Several groups have postulated the use of p-type ZnO doped with nitrogen, arsenic or phosphorus7,8,9,10, and even p–n junctions11,12,13. However, the choice of dopant and growth technique remains controversial and the reliability of p-type ZnO is still under debate14. If ZnO is ever to produce long-lasting and robust devices, the quality of epitaxial layers has to be improved as has been the protocol in other compound semiconductors15. Here we report high-quality undoped films with electron mobility exceeding that in the bulk. We have used a new technique to fabricate p-type ZnO reproducibly. Violet electroluminescence from homostructural p–i–n junctions is demonstrated at room-temperature.
1,964 citations
TL;DR: In this paper, a new calculation following traditional methods is proposed for deducing optical constants and thickness from the fringe pattern of the transmission spectrum of a thin transparent dielectric film surrounded by nonabsorbing media.
Abstract: A new calculation following traditional methods is proposed for deducing optical constants and thickness from the fringe pattern of the transmission spectrum of a thin transparent dielectric film surrounded by non-absorbing media. The particular interest of this method, apart from its easiness, is that it makes a directly programmable calculation possible; the accuracy is of the same order as for the iteration method.
1,499 citations
TL;DR: In this paper, a Raman scattering study of wurtzite was carried out over a temperature range from 80 to 750°C, where the second-order Raman features were interpreted in the light of recent ab initio phonon density of states calculations.
Abstract: We present a Raman scattering study of wurtzite $\mathrm{ZnO}$ over a temperature range from 80 to $750\phantom{\rule{03em}{0ex}}\mathrm{K}$ Second-order Raman features are interpreted in the light of recent ab initio phonon density of states calculations The temperature dependence of the Raman intensities allows the assignment of difference modes to be made unambiguously Some weak, sharp Raman peaks are detected whose temperature dependence suggests they may be due to impurity modes High-resolution spectra of the ${E}_{2}^{\mathrm{high}}$, ${A}_{1}(\mathrm{LO})$, and ${E}_{1}(\mathrm{LO})$ modes were recorded, and an analysis of the anharmonicity and lifetimes of these phonons is carried out The ${E}_{2}^{\mathrm{high}}$ mode displays a visibly asymmetric line shape This can be attributed to anharmonic interaction with transverse and longitudinal acoustic phonon combinations in the vicinity of the $K$ point, where the two-phonon density of states displays a sharp edge around the ${E}_{2}^{\mathrm{high}}$ frequency The temperature dependence of the linewidth and frequency of the ${E}_{2}^{\mathrm{high}}$ mode is well described by a perturbation-theory renormalization of the harmonic ${E}_{2}^{\mathrm{high}}$ frequency resulting from the interaction with the acoustic two-phonon density of states In contrast, the ${A}_{1}(\mathrm{LO})$ and ${E}_{1}(\mathrm{LO})$ frequencies lie in a region of nearly flat two-phonon density of states, and they exhibit a nearly symmetric Lorentzian line shape with a temperature dependence that is well accounted for by a dominating asymmetric decay channel
1,217 citations